1. Field of the Invention
The present invention relates to a method used in a wireless communications system and related communication device, and more particularly, to a method of handling positioning measurement corresponding to a mobile device in a wireless communications system with relay deployment and related communication device.
2. Description of the Prior Art
A long-term evolution (LTE) system, initiated by the third generation partnership project (3GPP), is now being regarded as a new radio interface and radio network architecture that provides a high data rate, low latency, packet optimization, and improved system capacity and coverage. In the LTE system, an evolved universal terrestrial radio access network (E-UTRAN) includes a plurality of evolved Node-Bs (eNBs) and communicates with a plurality of mobile stations, also referred as user equipments (UEs). The UE of the LTE system can transmit and receive data on only one carrier component at any time.
For certain reason, such as emergency consideration, several positioning methods are developed for UE positioning estimation. Positioning methods supported within the E-UTRAN include cell identity (ID) based method, observed time difference of arrival (OTDOA) method, network-assisted Global Navigation Satellite System (GNSS) method, etc. Please note that, the OTDOA positioning method may be assisted by network configurable idle periods (namely OTDOA-IPDL), in order to potentially improve the hearability of neighbouring eNBs. The OTDOA positioning method involves measurements made by a UE, and the measurement results are then sent to the network (e.g. E-UTRAN) for UE positioning estimation.
During positioning measurement, the UE monitors various types of reference signals (e.g. cell state information reference signals (CSI-RS) or cell reference signals (CRS)), and detects arrival times of the reference signals from different cells (e.g. eNBs). After that, the UE generates a measurement report including the arrival times of the reference signals from different cells measured at the UE, and then sends the measurement report to the network. Thus, the network performs the UE positioning estimation based on the measurement report.
A long term evolution-advanced (LTE-A) system, as its name implies, is an evolution of the LTE system, with coordinated multipoint transmission/reception (COMP) and relay deployment. The COMP is considered for LTE-Advanced as a tool to improve coverage of high data rates, cell edge throughput, and system efficiency, which implies dynamic coordination among multiple geographical separated points. That is, when an UE is in a cell-edge region, the UE is able to receive signal from multiple cells, and the multiple cells can receive transmission of the UE.
In addition, a relay node in the LTE-A system is considered to improve the coverage of high data rates, group mobility, temporary network deployment, the cell-edge throughput and to extend coverage. The relay can be deployed at the cell edge where the eNB may not be unable to provide required radio quality/throughput for the UEs that shall be served by the eNB or at certain location where radio signals of the eNB may not cover.
Thus, in the LTE-A system, the UE may simultaneously have links with the eNB and the relay capable of communicating with the eNB when the UE is under both coverage of the eNB and the relay. In addition, transparency of the relay can affect data transmission of the links. That is, with deployment of a transparent relay, the UE is not aware of whether or not the UE communicates with the E-UTRAN with the relay. With deployment of a non-transparent relay, the UE is aware of whether or not the UE communicates with the E-UTRAN with the relay.
However, without consideration with the relay deployment and the COMP in the LTE system, several scenarios are described as follows.
In the first scenario, since the relay deployment is not considered in the LTE system, the LTE system does not consider what role the relay node plays in the positioning measurement. In other words, the LTE system does not specify how the relay node involves in the positioning measurement. Therefore, the UE in the LTE-A system does not know how to perform the positioning measurement with the relay node, when following the LTE specifications, causing measuring problems, especially when time alignment and scheduling rule are not considered yet.
In the second scenario, the UE generates the measurement report based on measurement results associated with the reference signals transmitted from the eNBs. However, within the relay deployment, the UE may generate a measurement report according to a reference signal transmitted from the relay or base station. Currently, the LTE-A system does not specify how the network shall deal with the measurement report associated with the relay.
In the third scenario, the UE transmits the measurement report on an uplink grant when the positioning measurement is completely performed. However, due to the need of accumulation of reference signals under consideration of channel condition, decoding performance, performance accuracy and reference signal pattern, the UE may not be able to finish the positioning measurement before transmitting the measurement report on the uplink grant. The LTE-A system doest not clear define how the UE shall deal with this situation.
In the fourth scenario, the UE performs the measurements (e.g. channel quality measurement, positioning measurement or mobility measurement) within a measurement gap. In the LTE system, a length of the measurement gap is defined as 6 ms at downlink (DL) and 7 ms at uplink (UL). However, with the relay deployment in the LTE-A system, continuous uplink/downlink transmission/reception opportunities are not feasible due to interference consideration of inband relaying operation, and thereby the UE may not perform measurements during a certain subframe or period even though the measurement gap is configured to the UE. Generally, no data reception and transmission can be performed during a period of the measurement gap. Due to possible backhaul downlink reception for inband relaying operation during the measurement gap, the length of the measurement gap for the measurements with the relay deployment shall be reconfigured, so as to avoid transmission efficiency degradation (e.g. UE cannot actually receive anything on certain subframes during 6 ms measurement gap where UE may make use of these subframes for transmission at uplink). In addition, how the UE shall behave during no transmission (e.g. due to discontinuous uplink/downlink transmission opportunities) if the measurement gap is configured shall be a topic for discussion.
In the fifth scenario, both the CSI-RS and the CRS can be utilized for channel quality measurement in the LTE-A system. However, for the COMP operation, the LTE-A system does not define whether the UE can average the measurement result of both the CSI-RS and the CRS for the measurement report and whether the UE can measure different reference signal types (e.g. the CSI-RS and the CRS) from different cells in the COMP operation. Moreover, with current measurement report structure, the network may not know which type of the reference signal the UE was measured when receiving the measurement report from the UE. In addition, LTE-A system does not define whether different reference signal types use the similar transmission power. Since the CSI-RS and the CRS use different reference signal densities or periods, the CSI-RS and the CRS may require different transmission power for transmission. Without knowing the measured reference signal type, the network does not know what transmission power control shall be applied for the measured reference signal type.
In the sixth scenario, when the network configures the UE with the COMP operation, the UE may not have enough time to complete the positioning measurement for all active cells in the COMP operation within a measurement gap. Or, the measurement gap for measuring all active cells may be extremely long, thereby impacting transmission delay and efficiency. However, the LTE-A system does not specify how to deal with this situation.
In addition, since CoMP operating set (e.g. all cells prepared for the UE in advance) is equal or larger than CoMP active set (e.g cells participating the transmission), the rest of cells not in CoMP active set should be able to utilized for UL transmission during measurement gap for cells in active set.
Otherwise, the measurement gap should be configured for part of active cells (e.g. full measurement gap or part of measurement gap first in average) so that the rest of active cells not being measured could serve UE (e.g. take turns).
In addition, it's not clear how network decide to configure measurement gap due to different CSI-RS/CRS periods and patterns among active cells.